1. Field of the Invention
The present invention relates generally to the field of high oxygen barrier polymers. More particularly, it concerns a modified vinyl alcohol polymer (mPVOH), or blends comprising the mPVOH, used as an oxygen barrier for food and beverage packaging applications, methods of making the mPVOH, packaging articles comprising the mPVOH, and methods of making the packaging articles.
2. Description of Related Art
Limiting the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and shelf-life of the product. For instance, by limiting the oxygen transmission from environment into the oxygen sensitive food products in a packaging system, the quality of the food product can be maintained, and food spoilage can be avoided. In addition, high oxygen barrier packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and restocking.
Plastics continue to expand into food packaging applications traditionally served by metal and glass materials. An important packaging application area for polymeric materials is in packaging oxygen-sensitive food and beverage products. Polymers used for these applications, either as films or rigid containers, can be classified by their relative permeation to oxygen. It can be desirable to prepare packaging materials from polymers having low oxygen permeation, i.e., so called “gas barrier” polymers. Of the many classes of polymers for such applications, those generally held to be high oxygen barrier materials include polyvinylalcohol (PVOH), poly(ethylene vinyl alcohol) (EVOH), poly(vinylidene chloride) (PVDC), and acrylonitrile polymer (PAN). The barrier polymers generally classified as moderate to intermediate include aromatic nylon and amorphous nylon. Among the high oxygen barrier resins, the use of poly(ethylene vinyl alcohol) (EVOH) copolymers shows the most rapid growth. EVOH is commercially available in several grades with different ratios of ethylene/vinyl alcohol in the polymer chain. Familiar containers comprising an EVOH oxygen barrier include squeezable bottles (e.g. for ketchup or other condiments), shelf-stable entree container, and, more recently, beer bottles. However, the oxygen barrier properties of high barrier polymers, such as EVOH, are still frequently not as high as glasses or metals for a wide range of packaging applications. This performance gap between high barrier polymers and glasses or metals represents a tremendous opportunity in both rigid and flexible packaging applications; this has prompted intensive effort in the field to improve the oxygen barrier performance for EVOH barrier materials.